1. Field of the Invention
The present invention relates to a multilayer golf ball having at least four layers and having excellent durability and a good "feel" when hit with a golf club.
2. Related Art
A number of approaches have been tried to enhance the feel and distance of solid golf balls composed of a solid core and a cover. One such approach has been to increase the number of layers in the ball. For example, JP-A 10-127819 discloses a golf ball wherein the solid core is formed to a three-layer construction of an inner layer, an intermediate layer, and an outer layer. The inner and outer layers are each made of rubber compositions, and the intermediate layer is composed of a thermoplastic elastomer, typically thermoplastic polyamide elastomer. These choices are made in order to provide improved distance and a soft feel.
Similarly intending to provide a good feel and improved distance, JP-A 10-179797 discloses a golf ball that has a four-layer construction comprising two inner and outer intermediate layers situated between a "center" serving as the core and a cover which corresponds to the ball's surface. The thickness and JIS-C hardness ranges are prescribed for each layer. Essentially, the inner intermediate layer made of ionomer resin is situated between the core and the outer intermediate layer made of rubber compositions as illustrated in the examples of this reference.
The above art attempts to enhance the feel and distance of a golf ball by increasing the number of layers and specifying the material and hardness for each layer.
However, in these prior-art golf balls, providing larger differences in hardness between the respective layers so as to further enhance performance tends to lead to stress concentration at the boundary surfaces between the layers, making the ball more prone to failure when hit. This problem is most acute in balls that use a rubber material in the intermediate layer to achieve relatively good resilience.